1. Field of the Invention
This invention relates to monomers and polymers containing imine functional groups (also known as Schiff bases), methods of making such monomers and polymers, and methods of using them in various applications, such as medical devices.
2. Description of the Related Art
Biodegradable polymers are widely used in the medical and pharmaceutical industries. When determining whether a polymer is suitable for use in these industries, the most important things to consider are the hydrolytic and thermal stability of said polymer. Other characteristics of a suitable polymer include said polymer being flexible, hydrophilic, degradable, non-immunogenic, additive compatible and non-toxic.
The tyrosine-derived monomers of U.S. Pat. No. 5,099,060 polymerize to form polymers with higher melt or solution viscosities that may result in poor processibility. As a result, the fabrication of the polymers requires higher temperatures, higher pressures, or both, which are less economical and may also degrade the polymer or any additives (such as biological or pharmaceutical moieties).
Such higher melt or solution viscosities can occur with tyrosine-derived polymers such as the polyiminocarbonates of U.S. Pat. No. 4,980,449, the polycarbonates of U.S. Pat. No. 5,099,060, the polyarylates of U.S. Pat. No. 5,216,115, the poly(alkylene oxide) block copolymers of U.S. Pat. No. 5,658,995, the phosphorous-containing polymers of U.S. Pat. Nos. 5,912,225 and 6,238,687, the anionic polymers of U.S. Pat. No. 6,120,491, the poly(amide carbonates) and poly(ester amides) of U.S. Pat. No. 6,284,862, the radio-opaque polymers of U.S. Pat. No. 6,475,477, and the polyethers of U.S. Pat. No. 6,602,497. The disclosures of all the foregoing patents are incorporated herein by reference in their entirety.
There exists a need for polymers with lower melt viscosities that are capable of being melt-processed and/or solution processed with greater ease, lower temperatures and/or pressures.